When machining the journal of a crankshaft, in order to be able to cut a 90° corner, this journal must first be machined with a first cutting plate before the cylinder surface is then machined by means of a so-called diameter plate. Productivity is relatively low if two different indexable inserts, each with four cutting edges, are used for these machining processes.
U.S. Pat. No. 6,227,772 describes a cutting insert having a largely parallelepipedal base body that is fitted as an indexable insert with eight usable cutting plates. This cutting insert has two planes arranged parallel to one another and larger surfaces through which pass a fastening hole and four side faces adjacent thereto, specifically two small end faces that are parallel to one another and larger longitudinal faces that each have, in the center approximately along their longitudinal axis, a projecting bar that acts as a support surface when clamping the cutting insert into a tool holder. The larger surfaces merge via a rounded edge into smaller edge surfaces so that on the longitudinal side approximately quarter circle-shaped cutting edges result as limit lines to the edge surfaces in the corner area. The long cutting edges as limit lines as [sic] between the larger surfaces and each adjacent longitudinal surface are arcuately curved so that a body results that is mirror-symmetrical to the longitudinal center plane and to the transverse center plane. With each of their ends and the rounded edge, the long cutting edges form an angle between 70° and 80° between the small edge surface and the larger surface. Despite these eight cutting edges, it is not possible to cut 90° corners with such a cutting insert because the secondary cutting edges would re-cut the cheeks of the 90° corner. Thus the use of these cutting plates is also limited to the use of four cutting edges.